Harper was shown a straight red card and Porter fired home from the spot.

After Tom Lowery had struck the hosts' woodwork, Rovers were then reduced to nine men when Elliott Bennett was sent off after 56 minutes following a clash with Crewe's Perry Ng - and, within 10 minutes, Crewe were level.

Eddie Nolan headed home after a corner caused chaos in the box and Porter nodded in George Cooper's cross to level with his ninth goal of the season.

But, despite some at times desperate defending, the two sides could not be separated and so both go into Monday's third-round draw - and on to a replay at Gresty Road on Tuesday, 12 December.

Blackburn manager Tony Mowbray told BBC Radio Lancashire:

"It could have been any score you wanted to pick after 20 minutes, we were playing that well. But, obviously, the first sending off and the penalty was the changing point.

"In my opinion, it wasn't even a foul. They were grappling each other and the boy goes down, so for them to get a penalty and a sending off seems really harsh.

"I haven't seen the Elliott Bennett one again yet. Referees get paid to make decisions and he's made a lot, but we have to bide by them and get on with it.

"Give Crewe some credit. They grasped hold of the hope they were given. But we have to take the positives, we're still in the FA Cup and, when it was 11 v 11, the gulf was there for all to see."

Crewe manager David Artell told BBC Radio Stoke:

"An enthralling cup tie. The media say the magic of the FA Cup is diminished. But, while it might be so for the Premier League clubs who play their reserve teams, it's not in League One and League Two.

"It's a chance missed. It could have been even better for us but, if I'd been asked after 20 minutes whether I'd take a replay I'd have snatched your hand off.

"We never got within five yards of them in the first 20 minutes but we then pressed them high up the pitch and that's what we had to do.

"The character and belief shown by the players was great. I'm so proud that we came back from three down. It doesn't happen very often in football, never mind at Crewe."